Draining an old plaster pool for repairs... understanding risks

[radtfp]

I know that draining is often dependent on location, type of pool, and weather. It is a very context specific question and answer.

But I am hoping to receive some kind of foundational advice here. I have drained my ~40 year old plaster pool about halfway to make some repairs to the light, diagnose a leak, and attempt to replace the calcium-caked metal return eyelets.

The water table is about 40-50ft underground. It is a 8ft deep pool, rectangular, sloped to 4ft in the shallow end, with a jacuzzi in a corner.

It is my understanding that plaster was often mixed with asbestos 40 years ago, and is therefore a bit stronger than mixes today. Please correct me if I am wrong here.

On close inspection of the plaster, I can see it was mixed with some kind of aggregate. Looks like granules of marble or another shiny/tumbled stone.

Right now it is October, and temperature highs range in the 80s-90s. Relative humidity is around 50%.

Here are my questions:

• If I drain my pool for 7 days, what risks do I need to accept?
• If I drain my pool for 21 days, what risks do I need to accept?
• What physical attributes of gunite/plaster change when it dries out?

Thank you

 

[ajw22]

Welcome to TFP.

How long have you been in the house?

Do you really think that the plaster in the pool is original from 40 years ago?

When plaster dries out it can develop spider cracks as it shrinks. The cracks may close up when the plaster gets hydrated again.

Do you have a hydro static drain in the bottom of your pool?

Do you have hydro static plugs in the bottom of the pool that can be removed while it is empty? That would remove the risk of ground water from a storm popping the pool out of the ground.

Pools are often drained for maintenance. If your pool needs work then you just have to hope for a good outcome.

@AQUA~HOLICS is in your area and may have thoughts.

 

[Bperry]

I know that draining is often dependent on location, type of pool, and weather. It is a very context specific question and answer.

But I am hoping to receive some kind of foundational advice here. I have drained my ~40 year old plaster pool about halfway to make some repairs to the light, diagnose a leak, and attempt to replace the calcium-caked metal return eyelets.

The water table is about 40-50ft underground. It is a 8ft deep pool, rectangular, sloped to 4ft in the shallow end, with a jacuzzi in a corner.

It is my understanding that plaster was often mixed with asbestos 40 years ago, and is therefore a bit stronger than mixes today. Please correct me if I am wrong here.

On close inspection of the plaster, I can see it was mixed with some kind of aggregate. Looks like granules of marble or another shiny/tumbled stone.

Right now it is October, and temperature highs range in the 80s-90s. Relative humidity is around 50%.

Here are my questions:

• If I drain my pool for 7 days, what risks do I need to accept?
• If I drain my pool for 21 days, what risks do I need to accept?
• What physical attributes of gunite/plaster change when it dries out?

Thank you

Asbestos was well out of favor by the 1980’s so I’d assume you are pretty safe there, though I’ve never heard of it being used in pool plaster. Still not good to breathe plaster dust, cement dust, any kind of dust.

 

[radtfp]

Welcome to TFP.

Thanks! Long time lurker here.

How long have you been in the house?

Do you really think that the plaster in the pool is original from 40 years ago?

Family home. I know the plaster is at least 20 years old, and the pool itself is at least 30. 40 is a liberal estimate. It was built by a company called Omega Pools. I unfortunately lack the paperwork for any more details.

When plaster dries out it can develop spider cracks as it shrinks. The cracks may close up when the plaster gets hydrated again.

Got it, makes perfect sense. Is the gunite behind the plaster typically affected?

Do you have a hydro static drain in the bottom of your pool?

Do you have hydro static plugs in the bottom of the pool that can be removed while it is empty? That would remove the risk of ground water from a storm popping the pool out of the ground.

I will be inspecting this today. There is a small circular drain at the bottom. I will open it up to see if there is a valve or plug.

Pools are often drained for maintenance. If your pool needs work then you just have to hope for a good outcome.

This is good to know. I know nothing is 100%. But I would like to approach it with some wisdom, intelligence, forethought.

@AQUA~HOLICS is in your area and may have thoughts.

Thank you for the reference. I may stop by a local pool supply store, Tustana, for any of their thoughts.

 

[ajw22]

Is the gunite behind the plaster typically affected?

The gunite encased rebar shell is not affected by draining.

 

[radtfp]

Asbestos was well out of favor by the 1980’s so I’d assume you are pretty safe there, though I’ve never heard of it being used in pool plaster. Still not good to breathe plaster dust, cement dust, any kind of dust.

After a bit of research, I am 90% sure it is a "Marblesheen" or "Marbelite" pool.

 

[AQUA~HOLICS]

Typically hydrostatic valves are only seen in beach communities and even then only when water is visibly seen during the excavation. Have seen many pools at the Shotcrete stage during the rainy season and no problems from not having a hydrostatic valve.
Tustana pools in Tustin? That pool store has been around a long time. Personally not familiar with a high water table in that area.
All plaster types are not to be exposed to air for long periods of time.
The Shotcret/Gunite will not be effected by being exposed to the air.
If you need a contact number for a plaster company in your area PM me, Ray.

 

[radtfp]

I am confirming that there is no hydrostatic valve in this one. Yes Tustin area.

 

[Dirk]

After watching my plaster blister and pop off from a drain and acid wash, I will never drain my pool again if I can help it. I lowered it a bit this year, and immediately refilled it. (I just needed to rid my water of some built up calcium.)

Two things to consider. (1) The drying out of the plaster, as others have mentioned. And (2), this little tidbit: the water is part of the structure of a pool. This is more true of fiberglass and vinyl pools, of course, but it is nevertheless also somewhat true of plaster pools. The weight and pressure the water is exerting on the plaster is enormous. In some cases, especially with older plaster, it may be only that pressure that is holding weak plaster in place. If you suddenly remove that pressure, and then subject the plaster to dry air and sun, you're just asking for trouble.

You'll only know if your plaster is going to fail after it happens. No one here can predict how your plaster will react to this action, nor for how long you'll be able to get away with the missing water. But I think it is safe to claim: every minute your pool is empty (or lower) is increasing the risk.

As I mentioned, I would never drain a pool if I could help it. If I had to, I'd make a solid plan to do so for as short a time as possible. Like a few hours if I could, or a day at most. I'd plan to do so in the coolest weather possible, cloudy preferred. That plan would absolutely not be for 7 days, so you can guess what I'd say about 21 days.

Make a plan, have all your parts and materials ready to go. Line up some labor if you can't do the work yourself in a few hours. Postpone the drain until much closer to winter temperatures. And when you do drain, get it on, and get it done.

 

[Dirk]

PS. Whatever you do, don't acid wash the plaster while the pool is empty. More on that if you want the deets.

 

[Bperry]

I am confirming that there is no hydrostatic valve in this one. Yes Tustin area.

View attachment 533775

Is that a metal bottomed drain? What’s all the stuff at the bottom? It’s odd that the ring looks like normal PVC.

 

[MAPR-Austin]

Is that a metal bottomed drain? What’s all the stuff at the bottom? It’s odd that the ring looks like normal PVC.

Looks like they formed the sump when they shot the pool, the stuff on the bottom is stained plaster and rust coming from the shell/screws/anchors. The main drain ring is just set in the plaster.

@radtfp What is the topography around the pool? Soil type? It sounds like you would be safe as long as there isn't significant rain. You should try to get the pool refilled as soon as possible as a general rule.

 

[radtfp]

Looks like they formed the sump when they shot the pool, the stuff on the bottom is stained plaster and rust coming from the shell/screws/anchors. The main drain ring is just set in the plaster.

@radtfp What is the topography around the pool? Soil type? It sounds like you would be safe as long as there isn't significant rain. You should try to get the pool refilled as soon as possible as a general rule.

Yes both the spa and pool drains are pvc with some plaster filled in the bottom... yes it is kinda weird if you ask me. It is a rough surface. Rust is likely from rebar or any other metal parts set in there. Plumbing is copper.

Pool sits higher than the street, concrete deck with soil about an inch lower than that. Soil type is officially sandy loam, though the area is known to have clay which has cracked many foundations.

Thanks for all the advice here. I'll continue to update this thread as the project continues.

 

[MAPR-Austin]

Yes both the spa and pool drains are pvc with some plaster filled in the bottom... yes it is kinda weird if you ask me. It is a rough surface. Rust is likely from rebar or any other metal parts set in there. Plumbing is copper.

Pool sits higher than the street, concrete deck with soil about an inch lower than that. Soil type is officially sandy loam, though the area is known to have clay which has cracked many foundations.

Thanks for all the advice here. I'll continue to update this thread as the project continues.

It's not terribly uncommon. When I come across them I drill a hole in the bottom of the sump until we hit dirt/gravel/water. Plug with hydraulic cement when done.